Gypsum-based building material

ABSTRACT

A gypsum-based building material containing from 1 to 25% by weight of zeolites.

RELATED APPLICATION

This application is the National Stage of International Application No.PCT/EP2004/010208 filed Sep. 13, 2004, which claims the benefit ofEuropean Application No. 03020764.1 filed Sep. 12, 2003, and EuropeanApplication No. 03024922.1 filed Oct. 29, 2003, each of theseapplications is expressly incorporated by reference herein in itsentirety.

Gypsum-based building boards, for example, sandwich-type plaster boardsand gypsum fiber-boards, are employed in dry construction for thepreparation of floors, walls and ceilings.

Typical gypsum-based building boards have a core of cured calciumsulfate di-hydrate. It is coated with cardboard or non-woven(glass-fiber web). Typical thickness values are 6, 9.5, 12.5, 15 and 20mm.

For different intended applications, there are different optimizedboards, for example, boards having an increased moisture stability,boards having an increased fire resistance or a reduced soundtransmission property.

Plasters are coats on raw masonry or raw ceilings made of mortar. Ininterior construction, they often serve as a substrate for furtherdecoration, and on exterior walls, they serve as protection fromweathering.

There are also a wide variety of interior plasters which may be employedwithout further decoration, i.e., so-called decorative plasters.

It was the object of the present invention to provide building materialshaving improved properties. Surprisingly, it has been found thatgypsum-based building materials which contain from 1 to 25% by weight ofzeolites can lead to a reduction of airborne pollutants in interiors.Preferred zeolite contents are at least 5% by weight, more preferably atleast 10% by weight, and particularly preferred are the ranges of from 5to 20% by weight and from 10 to 15% by weight.

The contents are based on the proportion of zeolite in the driedgypsum-containing mass without, for example, cardboard or fibrouscontent.

According to the invention, it is particularly preferred to employnatural zeolites, i.e., zeolites which are not prepared synthetically(e.g., by reacting SiO₂-containing and Al₂O₃-containing substances withalkali hydroxides at temperatures of more than 50° C. in an aqueousphase). Thus, naturally occurring zeolites are those which are exploitedfrom deposits.

Suitable zeolites include, in particular, those which have a mineralphase composition selected from the group consisting of clinoptilolite,heulandite, chabasite, phillipsite, morderite and mixtures thereof.Astonishingly, the zeolites can be used not only in thermally activated,i.e., thermally dehydrated, but also in native forms.

In a particularly preferred embodiment, the zeolites are employed in anative form, i.e., without thermal activation or dehydration.

Astonishingly, activation of the zeolites apparently occurs during thepreparation/drying of the products. The dehydration of zeolites can bemeasured, for example, by thermogravimetric analysis (TGA).

FIG. 1 shows a TGA diagram for a naturally occurring zeolite. When thetemperature is increased, water is released over an extended range oftemperatures. The mass of the sample as a function of temperature andthe changes of mass (corresponding to the first derivative) are shown.

FIG. 2 shows a TGA diagram for a mixture of 90% by weight of stucco and10% by weight of naturally occurring zeolite. The mixture has beenadmixed with water and predried at about 40° C. after curing. The amountof water released as found in the TGA analysis corresponds to the amountof water in the gypsum; the water from the zeolite is not found (anylonger). The mass of the sample as a function of temperature and thechanges of mass (corresponding to the first derivative) are shown.

Nevertheless, such a zeolite shows the activity for the reduction ofairborne pollutants as required according to the invention.

The building materials preferably contain zeolites having a grain sizeof ≦200 μm, preferably smaller than 150 μm. This can be achieved mostsimply by fine milling.

Particularly suitable zeolites have d₅₀ values of from about 30 to about90 μm, more preferably from 40 to 70 μm.

The zeolites preferably have an oil number (determined in accordancewith DIN 53199) of at most 25 g/100 g of zeolite, preferably at most 10g/100 g of zeolite.

The materials employed according to the invention preferably containless than 3% of diatomaceous earth, and the zeolites are not admixedwith “antibacterial cations”.

Particularly preferred building materials are, on the one hand, buildingboards, especially sandwich-type plaster boards or gypsum fiber-boards,or plasters, especially plasters for applying to interior walls, morepreferably decorative plasters, because the admission of air is nothindered by further decoration in this case. The plasters preferablycontain the gypsum phase as a binder. The boards are coated, preferablywith cardboard or glass fiber web. If desired, they are also perforated(so-called “perforated boards”).

For a building board, stucco and zeolites, for example, may be mixed,and the finished board freed from excess water in a continuous dryer.

The gypsum content is preferably at least 30% by weight, more preferablyat least 50% by weight, even more preferably 70% by weight or more,respectively calculated on the cured mixture.

The present invention also relates to the use of the building materialsaccording to the invention for reducing airborne pollutants ininteriors. Airborne pollutants which can be successfully removed fromthe interior air include, for example, formaldehyde, benzene, ammoniaand tobacco smoke. Also smells, e.g., fishy smell, can be reduced, ascould be demonstrated experimentally by the degradation oftriethylamine.

Surprisingly, the airborne pollutants are not bound to the materials,but degraded/decomposed, so that no saturation of the materials occurs.

For formaldehyde, the maximum allowable working place concentration (MAKvalue) is 600 μg/m³. In a room where people smoke, the averageformaldehyde content is around 220 μg/m³ for an air-exchange rate of 0.5changes/hour. The WHO considers a guidance value of 100 μg/m³ for theprotection of health. A value to be sought in habitation is about 60μg/m³.

The average benzene content in a room where people smoke is about 45μg/m³ for an air-exchange rate of 0.5 changes/hour. A value to be soughtin habitation is <10 μg/m³.

By using the building materials according to the invention,correspondingly reduced values can be obtained.

The invention is further illustrated by the following Example.

EXAMPLE

Gypsum-based building boards containing 10% natural zeolites (native,i.e., non-dehydrated) with a grain size of at most 200 μm and a d₅₀value of 40 μm were laid in a room with a normal climate, resulting in1.23 m² of gypsum board area per 1 m³ of room volume. In this room, arespective noxious gas concentration with the noxious gases formaldehydeand benzene and with a noxious gas mixture from cigarette smoke wasadjusted by continuously supplying a defined mixture of noxious gases.The air-exchange rate of the respective mixture was 0.5 changes/hour,i.e., the mixture of noxious substances was renewed completely withintwo hours. In the exhausted mixture, the remaining concentration ofnoxious substances was measured as a gas concentration.

By the contact with the gypsum-based building boards, the major part ofthe noxious gases was degraded, and a concentration of noxious gases inthe system was obtained from a starting value (supplied mixture) to anequilibrium value (exhausted mixture)

for formaldehyde of 600 μg/m³ to  96 μg/m³; 220 μg/m³ to  40 μg/m³; forbenzene of  45 μg/m³ to <10 μg/m³.

For cigarette smoke, a substantial reduction of offensive smell from thecontact of the smoke with the gypsum-based building boards according tothe invention was additionally detected by olfactometry.

In the experimental series, it was additionally established that thenoxious substances were not deposited in the gypsum-based buildingboard, but reactively converted to harmless compounds.

Experiments with altered zeolite proportions in the gypsum-basedbuilding boards and altered formulations for the gypsum core, forexample, with the addition of 5% wood chips, provided similar results.

1. An interior finish building material comprising a gypsum-base building material composition for an interior finish, the composition containing from 1% by weight to 25% by weight of a naturally occurring zeolite, wherein the building material is a building board and wherein the building material has less than 3% diatomaceous earth and the naturally occurring zeolite is clinoptilolite.
 2. The building material of claim 1 wherein the composition contains at least 5% by weight of the zeolite.
 3. The building material of claim 1 wherein the composition contains at least 10% by weight of the zeolite.
 4. The building material of claim 1 wherein the composition contains from 5% by weight to 20% by weight of the zeolite.
 5. The building material of claim 1 wherein the composition contains from 10% by weight to 15% by weight of the zeolite.
 6. The building material of claim 1 wherein said zeolite has a grain size of ≦200 μm.
 7. The building material of claim 1 wherein said zeolite has a grain size of ≦150 μm.
 8. The building material of claim 1 wherein said zeolite has a d₅₀ value of from 30 μm to 90 μm.
 9. The building material of claim 1 wherein said zeolite has a d₅₀ value of from 40 μm to 70 μm.
 10. The building material of claim 1 wherein said zeolite is employed in a native form.
 11. The building material of claim 1 wherein the gypsum content is at least 30% by weight.
 12. The building material of claim 1 wherein the gypsum content is at least 70% by weight.
 13. The building material of claim 1 wherein the zeolite has an oil number of at most 25 g/100 g of zeolite.
 14. The building material of claim 1 wherein the zeolite has an oil number of at most 10 g/100 g of zeolite.
 15. The building material of claim 1 wherein the zeolites are not admixed with antibacterial cations.
 16. The building material of claim 1 wherein the zeolites are mixed with stucco.
 17. A method of using the building material of claim 1 to reduce airborne pollutants in interiors.
 18. The method of claim 17 wherein said airborne pollutants are selected from the group consisting of formaldehyde, benzene, ammonia, tobacco smoke and mixtures thereof.
 19. The building material of claim 1 characterized by being sandwich-type plaster boards or gypsum boards coated with a glass fiber web and optionally being perforated.
 20. The building material of claim 1 characterized by being a plaster in which calcium sulfate semihydrate is used as a binder. 